Presently, it is no longer acceptable to dump solid or soft paste-like residual and waste substances into waste sites due to existing environmental laws and regulations. As a result, the disposal of these materials has become vitally important to industries, government and consumers. Materials such as light shredded material from motor vehicles, plastics, lacquer and sludges such as solvent sludges and partially dewatered sewage sludge and the like are increasingly difficult and/or costly to dispose and pose a potential environmental problem.
Presently, low quality fuels, such as wet soft or brown coals having a high tar content, old tires, and the like can be gasified and disposed of without producing excessive levels of undesirable emissions in product gas and free or very nearly free of impurities which can reduce the heating value of the product gas, restrict the use of the gas in other processes, and pose significant hazards to the environment. One method of processing these materials is by using a shaft-type gasification reactor. Such reactors include a two or three layer charge bed in the primary gas chamber. The first layer of the charge bed consists of a relatively high-quality coke. The second layer of the charge bed includes a relatively thin layer of low quality fuel that lies on the first layer of the charge bed. The exposed surface of the second layer is arranged to face the primary gas chamber. The primary gas chamber is heated by fuel, oxygen, heated water, and/or steam. The primary gas chamber is heated to cause an endothermic gasification reaction. Materials such as waste oil and/or a paste-like residue from paper plant can be used as fuel for the primary gas burner. The heated gas that results from combustion of the waste oil and/or residue reaches a temperature of about 1500 to 1800.degree. C. The heated gas is directed to contact first layer of high quality coke and then the second layer of low quality fuel such as shredded tires. The endothermic reaction of the low quality fuel and heat gas forms a crude gas. The crude gas, which is formed, reaches a temperature of about 1864.degree. C. The crude gas exiting the gasification reaction is a gas having low levels of impurities. If a third layer is used in the gasification reactor, the third layer is a high quality coke that is similar to the first layer. Depending on the thickness of the low quality fuel second layer and on the adjustment of the primary gasification, the third layer, if used, will be gasified as the second layer and/or act as a filter for impurities for the crude gas passing through the third layer. The adjustment of the primary gasification is effected by regulating the ratio of oxygen to carbon carriers in the burner; by regulating the total quantity of primary gasification substances and/or in the event that pure oxygen is introduced through the burner in place of air, by way of the ratio of oxygen to steam. Such a gasifier is disclosed in EP 0 011 151 B1.
Tests conducted with the shaft-type gasifier disclosed in EP 0 011 151 B1 have shown that considerable problems arise during the high temperature gasification of a number of substances such as, for example, the light shredder fraction from a motor vehicle. In many cases, it is difficult to introduce this charge into the gasification zone, i.e., especially into the primary gas chamber, evenly enough that the product gas is of a sufficiently uniform quality. In the past, this problem was attempted to be solved by forming the charge into briquettes in order that it can be uniformally introduced into the shaft type gasifier. However, the process for producing the briquettes is extremely costly and there are many problems associated with the formation of the briquettes.
Another attempted solution, which has had little, if any success, relates to the grinding up the low quality fuel into relatively small particles and processing such fuel in a fly flow gasification reactor. This grinding procedure is problematic in that substances such as glass, stone, iron and others, which periodically damage the grinder, and fly flow gasification reactor are commonly present in the low quality fuel. Furthermore, these non-organic products impair the operation of a fly flow gasification reactor. In addition, the grinding process and use of a fly flow gasification reactor are extremely cost-intensive.
The disposal of waste materials of varying compositions that contain carbon, such as household garbage and industrial waste for producing a fuel gas is known from EP 0 120 397 A3. In this process, the carbon-containing waste is smoldered in a rotary tube reactor at more than 200.degree. C. to obtain a low temperature carbonized gas and pyrolysis coke. The pyrolysis coke is subsequently gasified in a fluid bed gasifier. The gasification products leave the gasifier at relatively low temperature typically between 400.degree. C. and 1000.degree. C. The liquid and the gaseous constituents released during the low temperature carbonization step and the gasification step are subsequently burned resulting in a substantial amount of ash which must be disposed of. This process results in a problem of environmentally disposing the ash. Furthermore, the process does not operate when processing materials such as a light shredder fraction from motor vehicles since such material include non-organic materials such as glass, metals, etc. A similar process as described in the EP 0 120 397 A3 is moreover known from the WO 90/02162 and has the same problems associated with the process of EP 0 120 397 A3.
In another waste disposal process which is described in the U.S. Pat. No. 4,497,637, the processing of various types of heterogenic substances is not suitable for processing and/or cannot be disposed of in an environment friendly manner. In this process, a synthetic gas is produced from a bio-mass such as wood chips. The bio-mass is formed by mechanical and thermic (drying) pre-treatment prior to the disposal of the materials. The pre-treatment is followed by a combined process of fly flow pyrolysis and fly flow gasification, both being performed in the so-called down-flow, whereby the fly flow pyrolysis takes place in an outer zone and the gasification takes place in an inner zone of a mutual concentrically constructed fly flow reactor. The pyrolysis is effected at a temperature of up to 870.degree. C. Thus, the temperature of the pyrolysis step is extremely high. Moreover, the hot carrier gas from the pyrolysis step contains nitrogen, water steam and CO2. The reaction pressure in the fly flow pyrolysis chamber ranges between 1 and 5 atmospheres under which a gasification of the mechanically and thermically pre-treated bio-mass begins. This waste disposal process includes a complicated pre-treatment step and complicated and costly pretreatment of the bio-mass prior to processing.
A similar process is disclosed in GB 2,109,400 A. The production of a synthetic gas results from a fibrous bio-mass, such as wood chips. After a pyrolytic pre-treatment of the bio-mass, a slurry gasification is carried out. This gasification requires a relatively high liquid carrier portion of approximately 40%. The gasification is effected at relatively low process temperatures, i.e. temperature below the softening point of the ashes. This process cannot process a wide variety of products.
Another process for disposing feed products containing carbon is disclosed in WO 81/00112. In this process of bituminous hard coal, brown coal, wood, straw are treated in a rotary tube pyrolysis. The process materials are then processed in a coupled crack and shaft gasification process by partially burning the low-temperature coke. Difficult process substances cannot be treated in this process.
In view of the deficiencies in the prior art to process waste components, there has developed a need to economically and environmentally dispose a wide variety of waste materials and to produce a process gas from organic materials which contains low levels of contaminants so that the product gas can be used safely as fuel in a wide variety of processes.